Problem About using ArrayList in C#

Question

4.00/5 (2 votes)

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Hello.

I have got a struct for ex:

C#

struct MyObject
{
    Point Location; 
    Color c;
}

And I am using an ArrayList for keep them together ex:

C#

ArrayList MyList = new ArrayList();
MyObject obj = new MyObject();
obj.Location = new Point(0, 0);
obj.c = Color.White;
MyList.Add(obj);

The problem is

I want to use an object's properties from ArrayList with specified index like:

C#

MyList[0].Location

but I have to convert MyList[0] to MyObject first. Because It is an Object type thats why I cannot reach MyObject's properties.

How can I do that?

Thanks.

(Btw) I do not want to use normal arrays because I will be using Add and RemoveAt functions a lot.

Posted 16-Feb-11 7:34am

amcanomer

Updated 16-Feb-11 7:39am

#realJSOP

v2

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3 solutions

Solution 3

C#

public struct MyObj
{
    public Point Location;
    public Color c;
}
public void test()
{
    List<MyObj> MyList = new List<MyObj>();
    MyObj[] abc = new MyObj[5];

    for (int i = 0; i < 5; i++)
    {
        abc[i].Location = new Point();
        abc[i].c = new Color();

        //to add in the List
        MyList.Add(abc[i]);
    }

    //gets the number of items in the List
    int count = MyList.Count;

    //gets the capacity of List
    int cap = MyList.Capacity;

    //Removes All elements from the List
    MyList.Clear();

    //inser the object at the specified index in List
    MyList.Insert(2, abc[3]);

    //removes the object from specified index
    MyList.RemoveAt(2);

    //Removes all elements from the List
    MyList.Clear();
}

Posted 16-Feb-11 8:52am

dontumindit

Updated 16-Feb-11 9:00am

v2

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Sergey Alexandrovich Kryukov · Accepted Answer · 2011-02-16T07:37:00

With classes like this you always will need type cast for collection's element.

In general case:

C#

object whoKnowsWhat //...
MyObject my = whoKnowsWhat as MyObject;
if (my == nulll) //... do something like throwing exception or ignoring
my./... use my

//If you're already sure is of the right class
//(and not null, already cheched), type cast directly:
MyObject my = (MyObject)whoKnowsWhat;
//if it's wrong, not problem, the code above will throw exception,
//so you could recover

Don't do all that in your case!

Simply don't use name space System.Collections, it's mostly obsolete; use System.Collections.Generic instead. At least you will be away from the problems with casting.

—SA

#realJSOP · Accepted Answer · 2011-02-16T07:40:00

Solution 2

Use a List<MyObject> instead. ArrayList is not going to let you do what you want to do.

Posted 16-Feb-11 7:40am

#realJSOP

Comments

Albin Abel 16-Feb-11 13:42pm

both answers are same, 5 each